Interaction between warfarin and cranberry juice

Warfarin is commonly used to treat or prevent thromboembolic events. Cranberry juice has been suggested to have an interaction with warfarin. However, there have been few reported cases of warfarin-cranberry juice interaction.

A 78-year-old, 86-kg man receiving warfarin at a total weekly dose of 45 mg for atrial fibrillation presented at the Bakersfield Healthcare Center of the VA Greater Los Angeles Healthcare System with an international normalized ratio (INR) of 6.45, having reported drinking a half gallon of cranberry/apple juice in the week prior to the elevated INR. After discontinuation of the cranberry juice, maintaining the warfarin dose for 5 days, and resuming the warfarin at a total weekly dose of 40 mg, the INR returned to the therapeutic range of 2 to 3.

Possible warfarin-cranberry juice interactions have been reported in the literature. Case reports illustrate INR elevation associated with cranberry juice ingestion concomitantly with warfarin administration and may be associated with bleeding (eg, pericardial, gastrointestinal). In the present case report, cranberry juice was the most likely cause of the patient's elevated INR. The Naranjo probability scale score was 3, suggesting that there was a possible interaction between warfarin and cranberry juice, while the modified Naranjo scale score adapted for anticoagulants was 5, rating the interaction as probable.

The combination of warfarin administration and cranberry juice ingestion appeared to be associated with an elevated INR without bleeding in this elderly patient.